1. Field of the Invention
The present invention relates, in general, to a receiving device in the teletext adaptor and, in particular, to a direct memory access control device of the teletext signal receiving apparatus which is usable as a part of the teletext adaptor.
2. Description of the Prior Art
Generally, the teletext broadcasting system means a newest broadcasting system which uses an interval of vertical blanking signal of the already established television broadcasting signal to transmit the teletext data, such as information of a letter or diagram. Also, for receiving the teletext broadcasting signal, a special apparatus, such as teletext adaptor, is required.
The teletext adaptor can be used by being connected with the ordinary television receiver. It is composed of a data separating device, a data receiving device and a data processing device. The data separating device separates the teletext data compounded within a vertical blanking interval of the composite video signal and supplies it to the data receiving device. A 36 byte signal corresponding to a data line is obtained during one interval of vertical blanking signal. The data line includes 3 synchronizing bytes and a control data. The control data is used for the transmission of teletext information. It consists of an error-preventing bit and address bits of information, etc.
The data receiving device divides real teletext data necessary for the data processing device. The data processing device reads such teletext data and supplies video composite signals for display on the screen of television receiver. However, the prior teletext adaptor requires to use a central processing unit to access memory for teletext information and it should have a large capacity which will, in turn, cause delay in data processing speed. Also, there are other shortcomings including high manufacturing cost and low reliability.
Therefore, it is an object of the present invention to provide a direct memory access control device to economize the manufacturing cost thereof.
Further, it is an object of the present invention to provide a direct memory access control device usable as a part of the highly reliable teletext adaptor.
Also, it is an object of the present invention to provide a direct memory access control device for teletext signal receiving apparatus usable as a part of the teletext adaptor.